1. Field of the Invention
The present invention relates to a plasmon-generator that generates near-field light, a thermally-assisted magnetic recording head that irradiates the near-field light to a magnetic recording medium to decrease an anisotropic magnetic field (coercive force) of the magnetic recording medium and then records data, and a head gimbal assembly and a magnetic recording device to which the head is used.
2. Description of the Related Art
In the field of magnetic recording using a magnetic head and a magnetic recording medium, further performance improvements of thin film magnetic heads and magnetic recording media have been demanded in conjunction with a growth of high recording density of magnetic disk devices. For the thin film magnetic heads, composite type thin film magnetic heads that are configured with a configuration in which a magnetoresistive (MR) element for reading and an electromagnetic transducer element for writing are laminated are widely used.
A recording layer of the magnetic recording medium is a discontinuous medium in which magnetic nanoparticles gather and each of the magnetic nanoparticles has a single magnetic domain structure. In the recording layer of the magnetic recording medium structured as described above, one recording bit is configured by a plurality of magnetic nanoparticles. Therefore, in order to increase recording density, asperities at a border between adjacent recording bits need to be reduced by decreasing the size of the magnetic nanoparticles. However, there is a problem that reducing the magnetic nanoparticles in size leads to a decrease in the volume of the magnetic nanoparticles, resulting in a decrease in thermal stability of magnetization in the magnetic nanoparticles.
As a countermeasure against this problem, increasing magnetic anisotropy energy Ku of magnetic nanoparticles may be considered; however, the increase in Ku causes an increase in an anisotropic magnetic field (coercive force) of the recording layer of the magnetic recording medium. On the other hand, the upper limit of the writing magnetic field intensity for the thin film magnetic head is substantially determined by saturation magnetic flux density of a soft magnetic material configuring a magnetic core in the head. As a result, when the anisotropic magnetic field of the recording layer of the magnetic recording medium exceeds an acceptable value determined from the upper limit of the writing magnetic field intensity, it becomes impossible to write.
Currently, as a method to solve such a problem of thermal stability, a so-called thermally-assisted magnetic recording method has been proposed in which, while a recording layer of a magnetic recording medium formed of a magnetic material with large Ku is used, the recording layer of the magnetic recording medium is heated immediately before the application of the writing magnetic field so that the anisotropic magnetic field is reduced and the writing is performed.
For the thermally-assisted magnetic recording method, methods in which laser light is utilized as a method of heating the recording layer of the magnetic recording medium are common. Among the methods, a method (near-field light heat application) is being a main stream in which laser light propagating through a waveguide is coupled with a plasmon-generator through a buffer layer therebetween in a surface plasmon mode so that surface plasmon is excited on the plasmon-generator; the surface plasmon is guided to the vicinity of a recording portion of the magnetic recording medium; and the medium is heated by near-field light generated from an end part (near-field light generation part) of the plasmon-generator.
The plasmon-generator used for the heat application system described above includes a near-field light generation part that is positioned on an air bearing surface (ABS), which is an opposing surface, of the magnetic recording medium and that generates the near-field light. And a detail description of a phenomenon in the technology is given. When the light propagating through the waveguide totally reflects off an interface between the waveguide and the buffer layer, evanescent light penetrating to the buffer layer is generated, the evanescent light couples with collective oscillation of charge, which is surface plasmon, on the plasmon-generator, and the surface plasmon is excited on the plasmon-generator. The surface plasmon excited on the plasmon-generator propagates through a propagation part (such as an edge of the plasmon-generator and a convex part) to a near-field light generation part, and near-field light is generated from the near-field light generation part positioned on the surface opposing the magnetic recording medium.
According to this technology, since the light propagating through the waveguide is not directly irradiated to the plasmon-generator, it is possible to prevent excessive temperature increase in the plasmon-generator. And then, such an element may be referred to as a surface evanescent light coupling type near-field light generator. Note, the near-field light is a sort of so-called electromagnetic field, which is formed around a substance, and has a physical property that can ignore a diffraction limit due to wavelengths of the light. The light having uniform wavelengths is irradiated to a microstructure body to form a near-field depending on a scale of the microstructure body. Thereby, it becomes possible to taper the light to a minimum region with a size of several tens of nm.
The head for thermally-assisted recording that can perform such heat application with the near-field light is configured to include a light waveguide, the plasmon-generator, and a magnetic pole for writing as principal elements thereof. The light waveguide is configured from oxide metals and/or nitride that introduce laser light. The plasmon-generator is configured from metals that generate plasmon. The magnetic pole for writing is formed of a magnetic material that generates a recording magnetic field.
And then, the thermally-assisted magnetic recording head that mounts such a plasmon-generator narrows a recording spot (track) width to enable the higher recording density to be realized.
Meanwhile, in order to suppress heat generation inside the plasmon-generator, materials with less plasmon loss should be selected as metals for generating the plasmon, which are materials of the plasmon-generator.
In the case when the heat generation inside the plasmon-generator is large, there is a threat not only that the magnetic head deforms (for example, protrusion of a tip part from the ABS) but also that the plasmon-generator itself may lose its shape due to migration of atoms of the material configuring the plasmon-generator. Accordingly, there is a concern that the head reliability is significantly affected. That is, in the case when the plasmon-generator deforms due to the heat generation, there is a threat that a preferred characteristic (heat application ability) is not obtained and a head characteristic is deteriorated.
In order to suppress heat generation, the plasmon-generator is preferably configured from a material with low dielectric loss å″ (material with a large value of optical extinction coefficient k and a small value of refractive index n). This is because the loss is decreased when the plasmon is propagated, and as a result, the light being converted into the thermal energy in the plasmon-generator is reduced.
As specific materials of the plasmon-generator with less loss, Au, Ag, Cu, Al, and an alloy made of these metals are given.
However, among the materials, Cu is unsuitable for a wafer process and manufacture process in manufacturing the magnetic head since Cu has corrosion against alkali resolution.
In addition, Al is unsuitable for the magnetic head with many processes exposing in the atmosphere since Al has corrosion against alkali resolution and at the same time the surface thereof oxidizes easily.
Although Ag simple substance has corrosion against alkali resolution, in the case when Ag system materials are configured as alloy materials of AgPdCu or AgBi, high corrosion resistance and high thermostability are obtained and change of optical constant is reduced. The Ag system materials are known to be used as reflection film materials for DVDs, for example. However, there is a threat that Ag oxidizes and the optical property deteriorates since the film surfaces of the Ag system materials are exposed in the atmosphere under a high temperature environment for the magnetic head and wafer process usage purpose.
Au system materials have excellent oxidation resistance and corrosion resistance, and are preferable materials for the wafer process. However, the Au system materials have poor heat resistance and may deform when heat is applied since the Au system materials themselves are soft and migrate easily.
From the point of view, the U.S. Patent Application Publication No. 2011/205,863, as related art, discloses that a near-field light transducer is configured containing gold (Au) and at least one dopant. The dopant is at least one selected out of Cu, Rh, Ru, Ag, Ta, Cr, Zr, V, Pd, Ir, Co, W, Ti, Mg, Fe, or Mo, and a dopant content thereof is in a range of 0.5%-30%. Also, it is disclosed that the dopant can be a nanoparticle oxide of V, Zr, Mg, Ca, Al, Ti, Si, Ce, Y, Ta, W, or Th, or a nanoparticle nitride of Ta, Al, Ti, Si, In, Fe, Zr, Cu, W or B. According to the proposal, improvement of mechanical intensity, heat resistance and durability is achieved by adding an appropriate amount of the dopant to a base of gold (Au).
However, it is inevitable that values of an optical extinction coefficient k and a refractive index n of the element itself vary by adding the dopant. Only with a simple method in which the dopant is added to the entire plasmon-generator simply formed by Au, the degree of heat generation in the element due to the addition tends to become larger. In the above-discussed situation, it is difficult to say that optimization of a configuration of the plasmon-generator is achieved.
In addition, the above-described prior art discloses a number of elements, oxide particles and nitride particles as dopants that may be added. However, in order to achieve the optimization of the configuration of the plasmon-generator and decrease a heat generation amount of the entire plasmon-generator, it is necessary to discuss the optimization of the configuration of the plasmon-generator and optimization of compositions including dopant selection. Especially, it is necessary to optimize by narrowing an area of a dopant that should be added to match to the configuration of the plasmon-generator and elements to be added.
It is objective of the present invention, which is invented under such situations, to provide a plasmon-generator that can satisfy thermostability, optical characteristic, and the process stability and has extremely excellent heat dissipation performance and heat generation suppression effect. In other words, it is objective of the present invention to provide a configuration and a composition material of the plasmon-generator that especially can suppress plasmon loss low, have excellent heat dissipation performance and heat generation suppression effect, and suppress deformation due to heat.
Note, JP Laid-Open Patent Application Nos. 2012-22768 and 2011-53531, JP Patent No. 4,007,702 and JP Laid-Open Patent Application No. H4-165085 are given as other prior arts related to the present invention. Descriptions regarding the arts are briefly given below.
JP Laid-Open Patent Application No. 2012-22768 discloses a thermally-assisted magnetic recording head including a plasmon-generator formed of a non-magnetic layer that contains one or more of Au, Ag, Cu, Al, Ti, Ta, and Ge. However, the above-described disclosed configuration has a different configuration and usage purpose from those of the present invention.
JP Laid-Open Patent Application No. 2011-53531 discloses that in a near-field light waveguide device including a near-field light waveguide part configured from a complex with a configuration where both a metal and an inorganic oxide are three-dimensionally continuous, a near-field light excitation part introducing near-field light to one end of the near-field light waveguide part and a near-field light output part outputting the near-field light from the other end of the near-field light waveguide part, the metal is composed of one metal selected from a group of Au, Ag, Cu, Al, Ni, Co, Cr, Sn, and Pd, or an alloy of these. The prior art absolutely discloses only that the waveguide is configured from a complex of the metal and the inorganic oxide (configuration where the metal is filled in micropores holed in the inorganic oxide). That metal is different from a metal member configuring the plasmon-generator itself.
JP Patent No. 4,007,702 discloses a sputtering target material for thin film formation, a thin film formed thereof, an optical recording medium, and a technology in which the antiweatherability is improved while Pd and/or Cu is/are added to Ag to maintain a reflective index of the film. However, the above-described disclosed configuration has a different configuration and usage purpose from those of the present invention.
JP Laid-Open Patent Application No. H4-165085 describes plating for ornament such as Au—Ni, Au—Co and, Au—Pd. However, this disclosure discloses only regarding the noble metal plating for general ornament, and the disclosure has a different configuration and usage purpose from those of the present invention.